The field of the invention relates to rotary impact drivers utilizing a rotary hammer intermittently engaging an anvil to produce a rotary impact force such as used in impact wrenches. In particular, the impact device of the invention is employed as an attachment for an electric drill.
Impact tools wherein rotary impact forces are sequentially applied to an output shaft are widely used to rotate threaded members such as wheel studs and nuts. Such rotary impact tools usually have an output shaft upon which various sizes of wrench sockets may be selectively mounted wherein the tool may be used to rotate nuts, bolts, screws, and the like.
The majority of rotary impact drive tools are operated by compressed air. However, it is known to also drive such tools by electric motors. Various types of drive mechanisms have been employed to convert the relatively uniform rotation of the motor to successively applied impacts capable of producing sufficiently high torque to accomplish the desired purpose. Such tools normally rotate an output shaft at a constant rate determined by the rate of rotation of the motor driven input shaft until the resistance to rotation of the output shaft reaches a predetermined value and, at such time, impact forces are rapidly applied to the output shaft to complete the tightening or loosening of a threaded member.
The drive mechanism for conventional motor driven impact devices may use springs, governors, centrifically operated weights, cams, etc., to convert the continuous rotation of the input shaft to the intermittent high torque rotation of the output shaft. While many known drive mechanisms are acceptable for use with air driven impact devices, such drive mechanisms as used with electric motors have not been capable of producing the higher torques often desired due the lower velocity of revolution of electric motors as compared with air motors.
To the applicant's knowledge rotary impact power driven tools presently available for both the compressed air driven type, or the electric type, are specially designed tools manufactured to be used only as rotary impact devices. Such tools are relatively expensive, and are usually only purchased for commercial use wherein the cost of such a specialized tool is justifiable. The part time or amateur mechanic does not require the use of an impact wrench or driver often enough to justify its expense. However, electric powered drills are commonly used by part time and amateur mechanics, but, to the applicant's knowledge, no attachment is available for such hand-held electric drills which is capable of permitting the drill to be used as an impact driver or impact wrench.